Sierra Rocio, Granda Cesar, Holtzapple Mark T
Artie McFerrin Dept. of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA.
Biotechnol Prog. 2009 Mar-Apr;25(2):323-32. doi: 10.1002/btpr.83.
Short-term lime pretreatment uses lime and high-pressure oxygen to significantly increase the digestibility of poplar wood. When the treated poplar wood was enzymatically hydrolyzed, glucan and xylan were converted to glucose and xylose, respectively. To calculate product yields from raw biomass, these sugars were expressed as equivalent glucan and xylan. To recommend pretreatment conditions, the single criterion was the maximum overall glucan and xylan yields using a cellulase loading of 15 FPU/g glucan in raw biomass. On this basis, the recommended conditions for short-term lime pretreatment of poplar wood follow: (1) 2 h, 140 degrees C, 21.7 bar absolute and (2) 2 h, 160 degrees C, and 14.8 bar absolute. In these two cases, the reactivity was nearly identical, thus the selected condition depends on the economic trade off between pressure and temperature. Considering glucose and xylose and their oligomers produced during 72 h of enzymatic hydrolysis, the overall yields attained under these recommended conditions follow: (1) 95.5 g glucan/100 g of glucan in raw biomass and 73.1 g xylan/100 g xylan in raw biomass and (2) 94.2 g glucan/100 g glucan in raw biomass and 73.2 g xylan/100 g xylan in raw biomass. The yields improved by increasing the enzyme loading. An optimal enzyme cocktail was identified as 67% cellulase, 12% beta-glucosidase, and 24% xylanase (mass of protein basis) with cellulase activity of 15 FPU/g glucan in raw biomass and total enzyme loading of 51 mg protein/g glucan in raw biomass. Ball milling the lime-treated poplar wood allowed for 100% conversion of glucan in 120 h with a cellulase loading of only 10 FPU/g glucan in raw biomass.
短期石灰预处理使用石灰和高压氧气显著提高杨木的消化率。当处理后的杨木进行酶水解时，葡聚糖和木聚糖分别转化为葡萄糖和木糖。为了计算原始生物质的产物产率，这些糖被表示为等效的葡聚糖和木聚糖。为了推荐预处理条件，唯一的标准是在原始生物质中使用15 FPU/g葡聚糖的纤维素酶负载量时，葡聚糖和木聚糖的最大总产率。在此基础上，杨木短期石灰预处理的推荐条件如下：(1) 2小时，140摄氏度，绝对压力21.7巴；(2) 2小时，160摄氏度，绝对压力14.8巴。在这两种情况下，反应活性几乎相同，因此所选条件取决于压力和温度之间的经济权衡。考虑到在72小时酶水解过程中产生的葡萄糖、木糖及其低聚物，在这些推荐条件下获得的总产率如下：(1) 原始生物质中每100克葡聚糖产生95.5克葡聚糖，每100克木聚糖产生73.1克木聚糖；(2) 原始生物质中每100克葡聚糖产生94.2克葡聚糖，每100克木聚糖产生73.2克木聚糖。通过增加酶负载量，产率得到提高。确定了一种最佳酶混合物，其组成为67%纤维素酶、12%β-葡萄糖苷酶和24%木聚糖酶（基于蛋白质质量），原始生物质中纤维素酶活性为15 FPU/g葡聚糖，总酶负载量为51 mg蛋白质/g葡聚糖。对经石灰处理的杨木进行球磨，在原始生物质中纤维素酶负载量仅为10 FPU/g葡聚糖的情况下，120小时内葡聚糖的转化率可达100%。
